It is known to achieve certain surface properties by providing resin rich surface layers, e.g., by lacquering. The finish and properties achieved depend on the properties of the lacquer used. Moreover, dust accumulated during the hardening period is a major problem in producing perfect, smooth and uniform surfaces, to which, for example, subsequent steps may be applied with predictable results. Lacquer coating is also completely inadequate to provide resin rich surface layers of the thickness generally required for the production of printed circuits.
It is also known to provide a resin rich surface layer on prints made on paper or other materials by laminating or gluing a suitable plastic foil to the surfaces of such materials. One of the main defects of this concept is the tendency to delaminate in use or after exposure to heat.
Additive processes to make printed circuitry require a uniform resin rich surface layer of at least 0.75 mil. (20 microns) thick to insure strong and uniform adhesion of electroless metal deposits and provide smooth surfaces for imaging processes. Heretofore, sheet sized laminates cut into panels (e.g., 4 .times. 8 feet) were coated individually by a variety of methods including roller coating, dip coating and curtain coating. Such methods lack thickness control and are difficult to use in production because of the need to handle a large number of sheets.
These and other disadvantages of the prior art are overcome by the present invention.